U.S. Pat. No. 5,357,239 granted to Ronald C. Lamparter Oct. 18, 1994 discloses actuating devices for safety devices such as safety gates and stop signs that are pivotally mounted on school busses. The actuating device comprises a housing and a bracket that is pivotally mounted to the housing. The bracket is pivoted by an electric motor that acts through a gear reduction unit, a drive member, a torsion spring and a spring engager. The electric motor is disposed in the housing along with an electronic control circuit that includes wiring harnesses, relays and mechanical limit switches.
U.S. Pat. No. 5,719,553 granted to Ronald C. Lamparter Feb. 17, 1998 discloses a sealed electrical actuator assembly for hinged vehicle safety devices that is an improvement over the actuating device of the earlier patent. In this assembly, the electric motor and the electronic control circuit including mechanical limit switches, relays and motor switches are enclosed in a compact, sealed, tamper proof housing that protects the components from vandalism and adverse weather conditions.
Improved stop signs and safety gates (also known as crossing arms) are disclosed in U.S. Pat. No. 5,634,287 issued to Ronald C. Lamparter Jun. 3, 1997 for an Illuminated Housing Assembly; U.S. Pat. No. 5,796,331 issued to Ronald C. Lamparter Aug. 18, 1998 for an Illuminated Pivotal Sign Assembly; and U.S. Pat. No. 5,687,500 issued to Ronald C. Lamparter Nov. 18, 1997 for a Stop Sign Housing with Flashing Lights. In these assemblies, the electric motor and the electronic control circuit including mechanical limit switches, relays and motor switches are also enclosed in a sealed outer housing.
U.S. Pat. No. 5,812,052 granted to Eric C. Swanger et al Sep. 22, 1998 discloses a switch operated actuating device for a school bus stop arm or crossing arm that includes a pair of beam generators and a pair of beam sensors in a switch housing and a rotatable plate. The rotatable plate which rotates with the stop arm or the crossing arm, is disposed in an opening in the switch housing. The beam generators are mounted in the switch housing on one side of the opening at 180 degree intervals. The beam sensors are mounted in the switch housing on the other side of opening directly in the paths of the beams generated by the respective beam generators. According to the Swanger '052 patent specification the beam generators and beam sensors preferably operate on the Hall effect principle by which the beam is in the form of a magnetic field extending between the beam generators and the sensors. Alternatively, a photo-electric system may be used by which the beam generated is a light beam and the sensor is a photo-electric sensor for sensing the presence of the light beam.
The rotatable plate has diametrically opposed full radius portions and diametrically opposed notches. According to the Swanger '052 patent specification, each of the sensors generate a first control signal when passage of the beam from the affiliated beam generator is blocked by full radius portions and a second control signal when the beam passes through the notches. One of these two signals is used to move the stop arm or the crossing arm between retracted and extended positions and the other signal is used to stop movement of the stop arm or the crossing arm.
According to the Swanger '052 patent specification, the arrangement shown in the Swanger '052 patent eliminates or ameliorates the drawbacks associated with actuating devices employing mechanical limit switches that operate in an unsealed and relatively inexpensive housing mounted on the vehicle. However, the arrangement of the Swanger '052 patent has several disadvantages. First and foremost, the Swanger '052 arrangement requires a rotatable plate which adds unnecessary expense and complexity. Moreover, precision in locating the safety device in the deployed position and the stored position is very difficult because such precision depends not only on the precise location of the generators and the sensors with respect to each other in the switch housing but also on the precise shape of the rotatable plate and the precise location of the rotatable plate with respect to the switch housing.
The rotatable plate is also exposed to the environment in an unsealed and relatively inexpensive housing mounted on the school bus and thus the rotatable plate is susceptible to weather damage, road hazards and vandalism, particularly in the case of a crossing arm or safety gate.
The Swanger arrangement is also difficult to assemble because the switch housing must span the axis of the motor unit and the output drive shaft of the motor unit must extend through the switch housing to a connection with the pivot arm for the safety device. Such assembly requires an adjustable mounting bracket for the motor unit which must be attached to the housing before the switch housing is attached to the flange of the housing. This adds further expense.
Another drawback in connection with the preferred use of the Hall effect principle is that the generators of the magnetic field are necessarily spaced from the sensors to make room for the intervening rotatable plate. This necessary spacing requires either stronger generators of the magnetic fields or more sensitive sensors or both furthering increasing cost.